ProjectSummary ThisapplicationproposestheWashingtonUniversityinSt.LouisSchoolofMedicine(WUSM)ModelOrganism ScreeningCore(wuMOSC)asakeyassetforPhaseIIoftheNIHUndiagnosedDiseasesNetwork(UDN).The wuMOSC will evaluate the pathogenicity of 200 genetic variants per year identified by UDN Clinical Sites in otherwise undiagnosed participants by leveraging the optimal combination of the following four animal model organisms and human cell-based Resource Cores: 1) C. elegans, 2) Drosophila, 3) zebrafish, and 4) human pluripotent stem cells (hPSCs). This multi-organism approach capitalizes on the experimental advantages of these four model systems, while avoiding the limitations of individual models. Extending the established advantages of the Drosophila and zebrafish, C. elegans allows for extremely rapid and cost-effective variant evaluation, while hPSCs enable assessment of genes and variants that are not conserved in animal models. AnexperiencedLeadershipTeamhasbeenassembledthatharnessesthecollaborativeresearchenvironment atWUSM,includingtheexpertiseoftheMcDonnellGenomeInstitute,andthesuperbWUSMclinicalpartners that constitute the proposed UDN Phase II WUSM Sequencing Center and Clinical Site applications, respectively. Using proven, cutting-edge, and novel bioinformatic approaches, combined with thoughtful considerationoftheadvantagesandlimitationsofeachmodelorganism,acarefulassessmentplanhasbeen definedfordeterminingtheputativepathogenicityofnominatedvariantsandprioritizingthemforexperimental evaluation by the Resource Cores. Preliminary data demonstrate that all four Resource Cores are using efficient and advanced genetic targeting techniques, including CRISPR/Cas9 to knock-in the human variant into an orthologous gene, knock-down and loss-of-function assays where appropriate, and overexpression to assess rescue of loss-of-function or for gain-of-function. Phenotypic analysis of the genetic models will be guided by information in model organism databases and the literature, as well as patient symptoms. This information will then be applied to the organism-specific and extensive phenotyping pipelines. The UDN Clinical Sites, Steering Committee, and Coordinating Committee will receive frequent communications regarding plans and results of the wuMOSC, through the activity of the Administrative Core, which will also disseminateacquiredmodelorganismexpertisetothewiderNIHandotherresearchcommunities. Therefore, themulti-modelorganismwuMOSCwillhaveanexceptionallyhighimpactonthediagnosticeffortsoftheUDN by bioinformatically and experimentally evaluating the potential of disease-causing variants in the context of disease-specificphenotypes.